Unfortunately, it depends.
I've bought about 900 books from Amazon.
But I only can load ca. 650 on my Paperwhite.
The rest is way too big:
Travel companions, due to the photos and maps.
Comics (Dilbert and Garfield).
Those easily have 50 or even 100MB each.
And then 2GB really is nothing.
Paperwhite, with its 2GB instead of the 4GB on former Kindles, is my first reader where I have to worry about memory.
First of all, I send books that I have read to the archive. Normally I'd keep them, but I can live with that.
Last but not least, I simply don't download books larger than 1 or 2MB. It's a pity, but those are more fun on Kindle Fire HD (= color) anyway, so I can live with that as well.
Still, I wish they would have granted 4GB. How much more would the price have been for another 2GB? 10 Euro?

Again, sorry for taking so long to come back to you. Althought I understand what you are saying, Harry, I have to go with mgmueller - reference books and books with over 1000 pages (and a considerable amount of pictures, though not many), between others, tend to take up quite some space, but, as other kindle users have done, I think I'll use something as Dropbox, Box or SugarSync and hope it all goes for the better